Thermal stability test apparatus for combustible fluids



April 18, 1967 L, ST|EFE| 3,314,282

THERMAL STABILITY TEST APPARATUS FOR COMBUSTIBLE FLUIDS Filed Feb. 5, 1965 2 Sheets-Sheet 1 6o Fig.2

INVENTOR.

LUDWIG SIEFEL BYW W).

" ATTORNEYS April 18, 1967 L. STIEFEL 3,314,282

THERMAL STABILITY TEST APPARATUS FOR COMBUSTIBLE FLUIDS Filed Feb. 15, 1965 2 s t .s 2

Stop Signal Start Signal rmer Switch o Line 220V. Line 4-. .J\

Solenoid Temp Valve Recorder N2 Cylinder Selector Vance Switch v Thermooouples/ 3 Controller Heater Pump Chamber Ionization v 220V Lme Probe Heater i 2 Vortac E O o C o 0 I50 8;

ms 190 zoo INVENTOR.

Temperature 0 BY LUDWtCihSTIEFEL W L. mu W ATTORNEYS United States Patent THERMAL STABILITY TEST APPARATUS FOR CGMBUSTIBLE FLUIDS Ludwig Stiefel, Philadelphia, Pa., assignor to the United States of -America as represented by the Secretary of the Armv Filed Feb. 3, 1965, Ser. No. 430,224 Claims. (Cl. 73-35) The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment to me of any royalty thereon.

This invention relates to an apparatus for testing the thermal stability of a combustible fluid, especially a liquid propellant. "As is readily understood in the combustible fluid art and particularly with regard to liquid propellants thermal stability thereof is defined as, the measure of a propellants ability to withstand significant chemical decomposition when exposed to elevated temperatures. The thermal stability of a propellant becomes very important when considering the environment to which a particular propellant is to be exposed. This is best understood by way of an illustrative application of a liquid propellant. Consider a liquid propellant which is to be used in a round of ammunition to be fired from an automatic weapon. A single round of ammunition proceeds automatically from a storage container into the weapon and finally is fired. As the weapon continues to operate it naturally becomes hotter. The relatively cold liquid propellant in a round of ammunition becomes subjected to a hot environment before being fired. The question then arises, how long may the propellant remain in the hot environment before it begins to chemically decompose or even ignite? If this question cannot be readily answered then possibilities of premature firing or misfiring of liquid propellant ammunition arises. In order to avoid this, preliminary testing of liquid propellants is conducted to establish their thermal stability characteristics. The data desired is generally in the form of a plot of points of temperature and time. a.

The curves show the magnitude of time to which a given propellant can be subjected to a temperature before it will ignite.

The accepted testing methods for determining the thermal stability characteristics of a given propellant were, either to place a capsule of propellant into a heated bath, or inject a sample of propellant into a relatively large heated chamber. In both cases time to ignition was measured. These two methods presented inherent disadvantages resulting in inaccuracies in data obtained. Namely, in the former method a time lag existed between the time the capsule itself was being heated and the time the propellant commenced heating. In the latter method the propellant would be completely vaporized when it was injected into the chamber which was not representative of an actual application. In both cases the time to ignition was obviously unreliable. Thus, what these above methods precluded was a simulation of a true environmental condition to which a given liquid propellant would be exposed, viz., a hot surrounding to which a cold propellant in a liquid state would he suddenly subjected and completely confined to prevent complete vaporization thereof.

Accordingly, it is an object of the present invention to provide an apparatus for testing the thermal stability of a combustible fluid, which test apparatus simulates true environmental conditions that a combustible fluid is likely to be exposed to.

It is another object of the present invention to provide an apparatus for testing the thermal stability of a combustible fluid, which apparatus can be heated to a desired "ice temperature while simultaneously maintaining a relatively cold propellant temperature.

-It is yet an object of this present invention to provide a thermal stability test apparatus which permits exposure of a cold liquid propellant in relatively entire liquid state to a relatively hot surrounding.

It is still an object of the present invention to provide a thermal stability test apparatus which is comprised of a uniformly heated test chamber communicating with a reservoir of cold fluid which is displaced into the'test chamber by a piston pump or the equivalent.

The foregoing and additional objects and advantages of the present invention will become apparent from the following detailed description thereof, consideration being given also to the attached drawings in which:

FIG. 1 is a side elevation view of a presently preferred embodiment of the invention; 1

FIG. 2 is a partial side view of FIG. 1 showing further details of construction;

FIG. 3 is a schematic representation of an illustrative system in which the present invention may be used;

FIG. 4 is a plot of data obtained by using the apparatus of the present invention.

Referring to the drawings in which like reference characters refer to like parts throughout 10 is the test apparatus as a whole which has a main body. 12 having a test chamber 14 therein. The test chamber 14 of this embodiment is a longitudinal passageway through the body 12. The volume of the test chamber 14 is carefully determined so that a volume of fluid equal to or less than the chamber volume will be placed therein. The significance of this will become readily apparent further along in this specification. The end portions of the test chamber 14 are closed by rupture discs 16 held in place by retainers 18 or the like, force fitted or screwed in the end portions of the body 12 as illustrated. The rupture discs 16 function as pressure relief means set to burst outwardly when a predetermined pressure is reached within the test chamber 14. Other pressure relief means may be used in lieu of the rupture discs 16, such as spring loaded pressure relief valves or the like.

At one end of the body 12 an open ended hollow body or cylinder 20 has its lower end in open communication with the test chamber 14. The cylinder 20 has its axis substantially normal to the surface of the body 12. The cylinder defines an internal space wherein a fluid may be stored, commonly called a reservoir 22. Disposed within the cylinder 20 and positioned normally above the reservoir 22 is a piston 24. As shown in FIG. 1 the piston 24 is in a ready position, that is a fluid is in the reservoir and the piston 24 is ready to move downwardly towards the test chamber 14 to displace the fluid. The piston 24 comprises a head 26 which has an outside diameter substantially that of the inside diameter of the cylinder, and a reduced diameter stem 28 which extends axially from the head 26 to a point without the cylinder 20. The stem 28 and head 26 define a continuous passageway 39 therethrough which provides a gas bleed channel for entrapped gas in the liquid combustibles stored in the reservoir 22. The stem 28 terminates in a cap or plug 32 screwed or force fitted thereon.

The upper end of the cylinder 20 contains a removable bushing 34 having an axial opening therethrough, through which extends the stem 28 of the piston 24. The bushing 34 is held in fixed relationship with the cylinder 20 by means of a pin 36 or the like extending through communicating openings in the bushing 34 and cylinder 20 wall. When it is desired to fill the reservoir 22 with a liquid the pin 36 is removed and the piston 24 drawn out of the cylinder 20, the piston 24 carrying the bushing 34 along with it. The liquid is then placed in the reservoir 22 and the piston 24, bushing 34 and pin 36 returned to their original orientation.

A channeled boss 38 or the like is provided on the periphery of the upper portion of the cylinder outer wall. The channel 443 communicates with the upper surface of the piston head 26. A pressurized gas such as dry nitrogen can be directed through the channel 40 by suitable plumbing (shown schematically in FIG. 3) to provide a driving force for the downward movement of the piston 24.

xThe piston head 26 and the bushing 34 are provided with seals 42 and 44 respectively such as O-rings for preventing any fluid leakage from the reservoir 22.

Interposed between the lower end of the cylinder 20 and the reservoir 22 is a spring acting ball type check valve 46. The check valve 46 body 48 rests on a reduced diameter portion of the cylinder 20 defining a shoulder 48. The check valve 46 is secured in place by means of a hollow retainer 50 force fitted or screwed into the cylinder 20 between the reservoir 22 and upper end surface of the check valve 46. When the piston 24 is urged downwardly through a fluid filled reservoir 22 a force is exerted through the ball valve 58 on the spring 52 which depresses the support stem 54 to depress the ball valve 58 opening the check valve 46 passageway 56 enabling the fluid to pass therethrough into the test chamber 14. When the pressure on the spring 52 is released the ball valve 58 reseats closing the passageway 56. The spring 52 also acts to urge the ball valve 58 against the valve seat portion of the passageway 56 wall to form a metal to metal seal. As can be readily understood the check valve 46 acts to permit unidirectional flow of fluid into the test chamber 14 only.

Rod type resistance heaters 60 are peripherally arranged in four equi-angularly spaced longitudinal openings in the body 12. This arrangement is clearly shown in FIG. 1 and FIG. 2. The heaters 60 are connected with a 220 v. A.C. source through suitable controllers as schematically shown in FIG. 3.

A cooling coil 62 is arranged about the outside wall of the cylinder 20 in a helical pattern. The coil 62 is conneeted to a source of coolant (not shown) which may be any fluid heat exchange medium suitable for maintaining a'particular fluid stored in the reservoir 22 at a desired temperature usually lower than that of the body 12.

In operation a liquid propellant is placed in the reservoir 22 as previously described. The reservoir 22 is bled via the passageway 30 of any entrapped gases to insure that only liquid propellants remain therein. The heaters 60 are turned on to bring the body 12 and test chamber 14 up to a desired steady state temperature. The propellant is maintained at a lower temperature than that of the test chamber 14 Walls by means of the coolant flowing through the coil 62. In' this embodiment the heaters 60 are controlled in two zones as shown in FIG. 3. The reason for this is that the portion of the body 12 in the vicinity of the cooled cylinder 20 will tend to lose heat more rapidly than the other portion thereof. The separate zoned heat control will act to provide a more uniform heating arrangement throughout the body 12 and consequently better temperature control.

When the desired test chamber 14 and propellant temperatures are reached the pressurized gas is allowed to flow into the cylinder 20 via the channel 40. The piston 24 is thus urged downwardly displacing the propellant into the test chamber 14. Time is recorded until the propellant ignites as will be readily apparent when the rupture discs 16 blow outwardly. A timer, as shown in the schematic of FIG. 3, is set to start when the piston 24 is activated and stop when the rupture discs 16 burst. Also as shown in FIG. 3 all temperatures are automatically recorded through a thermocouple circuit.

The volume of propellant displaced from the reservoir 22 into the test chamber 14 is metered by means of calibrated spacers 64 removably fixed to the piston stem 28.

The spacers 64 limit the displacement of the piston 24 and thus the volume of fluid into the test chamber 14.

The above described procedure is repeated at various temperatures. The data obtained can be transposed into a plot of time to ignition vs. chamber temperature. A typical plot'is shown in FIG. 4. This plot illustrates the thermal stability of a 60/40 ethyl propyl nitrate liquid propellant.

Resort may be had to the various modifications and variations which fall within the spirit of this invention and the scope of the appended claims.

I claim: 1. An apparatus for testing the thermal stability of a combustible fluid including a body defining a test chamber, said test chamber communicating with the outside of said body via at least one passageway;

means in said passageway for closing same said means being adapted to open when a predetermined pressure is reached within said test chamber;

a cylinder in open communication at one end with said test chamber, said cylinder defining a fluid reservoir;

means in said cylinder for filling said reservoir with a a removable fluid displacing means disposed within said cylinder;

means for heating said test chamber body; and

cooling means arranged around said cylinder for maintaining fluid therein at a relatively lower temperature than that of said test chamber body.

2. An apparatus for testing the thermal stability of a combustible fluid including a body defining a test chamber, said test chamber communicating with the outside of said body via at least one passageway;

means in said passageway for closing same, said means being adapted to open when a predetermined pressure is reached within said test chamber;

a cylinder in open communication at one end with said test chamber, said cylinder defining a fluid reservoir;

means in said cylinder for filling said reservoir with a a movable fluid displacing means disposed within said cylinder;

means within said cylinder for restricting fluid flow into said test chamber;

means for heating said test chamber body; and

cooling means arranged around said cylinder for maintaining fluid therein at a relatively lower temperaturethan that of said test chamber body.

3. An apparatus for testing the thermal stability of a combustible fluid including a body defining a test chamber, said test chamber communicating with the outside of said body via at least one passageway;

means in said passageway for closing same, said means being adapted to open when a predetermined pressure is reached within said test chamber;

a cylinder in open communication at one end with said test chamber, said cylinder defining a fluid reservoir;

means in said cylinder for filling said reservoir with a fluid;

a piston in said cylinder;

means for urging said piston toward the end of said cylinder which communicates with said test chamber whereby fluid' in said cylinder may be displaced into said test chamber;

adjustable means on said piston for metering the volume of fluid displaced into said test chamber;

means within said cylinder for restricting fluid flow into said test chamber;

means for heating said test chamber body; and

cooling means arranged around said cylinder for maintaining fluid therein at a relatively lower temperature than that of said test chamber body.

4. An apparatus for testing the thermal stability of a combustible fluid including a body defining a test chamber, said test chamber communicating with the outside of said body via at least one passageway;

means in said passageway for closing same said means being adapted to open when a predetermined pressure is reached within said test chamber;

a cylinder in open communication at one end with said test chamber, said cylinder defining a fluid reservoir;

a piston in said cylinder, said piston being removable from said cylinder to provide access to said reservoir for filling same with a fluid;

means for urging said piston toward the end of said cylinder which communicates with said test chamber whereby fluid in said cylinder may be displaced into said test chamber;

adjustable means on said piston for metering the volume of fluid displaced into said test chamber;

means within said cylinder for restricting fluid flow into said test chamber;

means for heating said test chamber body;

cooling means arranged around said cylinder for maintaining fluid therein at a relatively lower temperature than that of said test chamber body.

5. An apparatus for testing the thermal stability of a combustible fluid including a body defining a test chamber, said test chamber communicating with the outside of said body via two passageways;

rupture discs in each of said passageways said discs being adapted to rupture outwardly when a predetermined pressure is reached within said test chamber;

a cylinder defining a fluid reservoir, said cylinder being in open communication at one end with said test chamber and having a removable plug in its other end;

said plug defining a passageway therethrough coaxial with said cylinder;

a piston in said cylinder extending through said plug passageway to a point outside of said cylinder, said piston being removable with said plug from said cylinder to provide access to said reservoir for filling same with a fluid;

means for urging said piston toward the end of said cylinder which communicates with said test chamber to displace fluid into said test chamber;

adjustable means on said piston for metering the volume of fluid displaced into said test chamber;

a spring urged check valve disposed in said cylinder between said cylinder end which communicates with said test chamber and said reservoir, said check valve being adapted to allow fluid into said test chamber when said iston is urged toward said test chamber and to prevent any fluid flow from said test chamber into said reservoir;

means for heating said test chamber body;

cooling means arranged around said cylinder for maintaining fluid therein at a relatively lower temperature than that of said test chamber body.

6. An apparatus as defined in claim 5 wherein said piston communicates with a fluid pressure source which provides force suificient to urge said piston toward the end of said cylinder which communicates with said test chamber.

7. An apparatus as defined in claim 5 wherein said cooling means comprises a coil uniformly arranged in a helical pattern around said cylinder, said coil being connected with a source of cooling medium.

8. An apparatus as defined in claim 5 wherein said heating means comprises a plurality electrical resistance elements arranged in a uniform pattern peripherally in said test chamber body.

9. An apparatus as defined in claim 5 wherein said piston has an axial passageway therethrough for bleeding of entrapped gases from said reservoir.

10. An apparatus as defined in claim 5 wherein said metering means comprises at least one spacer movably fixed to said piston at a point outside of said cylinder, the thickness of said spacer limiting the displacement of said piston.

References Cited by the Examiner UNITED STATES PATENTS 2,789,428 4/ 1957 Mackas 7315 FOREIGN PATENTS 158,037 1/1964 Russia. 158,432 l/ 1964 Russia.

RICHARD C. QUEISSER, Primary Examiner.

J. GILL, Assistant Examiner. 

3. AN APPARATUS FOR TESTING THE THERMAL STABILITY OF A COMBUSTIBLE FLUID INCLUDING A BODY DEFINING A TEST CHAMBER, SAID TEST CHAMBER COMMUNICATING WITH THE OUTSIDE OF SAID BODY VIA AT LEAST ONE PASSAGEWAY; MEANS IN SAID PASSAGEWAY FOR CLOSING SAME, SAID MEANS BEING ADAPTED TO OPEN WHEN A PREDETERMINED PRESSURE IS REACHED WITHIN SAID TEST CHAMBER; A CYLINDER IN OPEN COMMUNICATION AT ONE END WITH SAID TEST CHAMBER, SAID CYLINDER DEFINING A FLUID RESERVOIR; MEANS IN SAID CYLINDER FOR FILLING SAID RESERVOIR WITH A FLUID; A PISTON IN SAID CYLINDER; MEANS FOR URGING SAID PISTON TOWARD THE END OF SAID CYLINDER WHICH COMMUNICATES WITH SAID TEST CHAMBER WHEREBY FLUID IN SAID CYLINDER MAY BE DISPLACED INTO SAID TEST CHAMBER; ADJUSTABLE MEANS ON SAID PISTON FOR METERING THE VOLUME OF FLUID DISPLACED INTO SAID TEST CHAMBER; 